Experiments, notes, &c. about the mechanical origine or production of divers particular qualities among which is inferred a discourse of the imperfection of the chymist's doctrine of qualities : together with some reflections upon the hypothesis of alcali and acidum / by the Honourable Robert Boyle ...

EXPER. X.

TIs very probable that further Trials will furnish us with more Instances to shew how the Pro∣duction of Cold may in some cases be effected, varied, or hinder'd by Mechanical Circumstances that are easily and usually overlook'd. I re∣member, on this occasion, that though

in the Experiment above recited we observ'd, that Oyl of Vitriol and wa∣ter being first shaken together, the volatil salt of Sal Armoniac being afterwards put to them, produced a sensible Coldness; yet I found, that if a little Oyl of Vitriol and of the vo∣latile Salt were first put together, though soon after a considerable pro∣portion of water were added, there would be produc'd not a Coldness, but a manifest degree of Heat, which would impell up the liquor in the Thermoscope to the height of some inches. And I remember too, that though Salt of Tartar will, as we shall see e're long, grow hot in the water, yet having distill'd some Salt of Tartar and Cinaber in a strong fire, and put the whole Caput mor∣tuum into distill'd or Rain-water, it made indeed a hissing there as if it had been Quick-lime, but produced no Heat, that I could by feeling per∣ceive. I shall adde, that not onely, as we have seen already, some un∣heeded Circumstances may promote

or hinder the artificial Production of Cold by particular Agents, but, which will seem more strange, some unobserv'd, and perhaps hardly ob∣servable, Indisposition in the Patient may promote or hinder the effects of the grand and Catholick Efficients of Cold, whatever those be. This sus∣picion I represent as a thing that fur∣ther experience may possibly coun∣tenance, because I have sometimes found, that the degree of the Ope∣ration of Cold has been much vari∣ed by latent Circumstances, some bodies being more wrought upon, and others less, than was upon very probable grounds expected. And particularly I remember, that though Oyl of Vitriol be one of the firiest liquors that is yet known, and does perform some of the Operations of fire it self, (as we shall elsewhere have occasion to shew) and will thaw Ice sooner than Spirit of Wine or a∣ny other liquor, as I have tried; yet having put about a pound or more, by our estimate, of choice rectified

Oyl of Vitriol into a strong Glass-Vial proportionable to it, we found, that, except a little that was fluid at the top, it was all congeal'd or co∣agulated into a mass like Ice, though the Glass stood in a Laboratory where a fire was constantly kept not far from it, and where Oyl of Vi∣triol very seldom or never has before or since been observ'd to congeal or coagulate so much as in part. And the odness of our Phaenomenon was increas'd by this Circumstance, that the Mass continued solid a good while after the weather was grown too mild to have such Operations upon Liquors far less indispos'd to lose their fluidity by Cold, than e∣ven common Oyl of Vitriol is. On the other side I remember, that a∣bout two years ago, I expos'd some Oyl of sweet Almonds hermetically seal'd up in a Glass-bubble, to ob∣serve what Condensation an intense cold could make of it, (for though Cold expands water, it condenses common oyl;) but the next day I

found to my wonder, that not onely the oyl remain'd unfrozen by the sharp frost it had been expos'd to, but that it had not its transparency troubled, though 'tis known, that oyl will be brought to concrete and turn opacous by a far less degree of Cold than is requisite to freeze water; notwithstanding which this liquor, which was lodged in a glass so thin, that 'twas blown at the flame of a Lamp, continued fluid and diaphanous in very frosty wea∣ther, so long till I lost the expectati∣on of seeing it congeal'd or concre∣ted. And this brings into my mind, that though Camphire be, as I formerly noted, reckon'd by ma∣ny potentially cold, yet we kept some oyl of it, of our making, wherein the whole body of the Camphire remain'd, being onely by some Nitrous Spirits reduc'd to the form of an Oyl; we kept it, I say, in such intense degrees of Cold, that would have easily frozen water, without finding it to lose its Trans∣parency

or its Fluidity.

And here I shall put an end to the first Section, (containing our Notes about Cold) the design of which may be not a little promoted by com∣paring with them the beginning of the ensuing Section. For if it be true, that (as we there shew) the nature of Heat consists either one∣ly or chiefly in the local motion of the small parts of a body Mechanically modified by certain conditions, of which the principal is the vehemen∣cy of the various agitations of those insensible parts; and if it be also true, as Experience witnesses it to be, that, when the minute parts of a body are in or arrive at such a state, that they are more slowly or faintly agi∣tated than those of our fingers or other organs of feeling, we judge them cold: These two things laid together seem plainly enough to ar∣gue, that a Privation or Negation of that Local Motion that is requisite to constitute Heat, may suffice for the denominating a body Cold, as Cold∣ness

is a quality of the Object, (which as 'tis perceiv'd by the mind, is also an affection of the Sentient:) And therefore an Imminution of such a degree of former motion as is ne∣cessary to make a body Hot as to sense, and which is sufficient to the Production of sensible Coldness, may be Mechanically made, since Slow∣ness as well as Swiftness being a Mode of Local motion is a Mechani∣cal thing: And though its effect, which is Coldness, seem a Privation or Negation; yet the Cause of it may be a positive Agent acting Me∣chanically, by clogging the Agile Calorific Particles, or deadning their motion, or perverting their determi∣nation, or by some other intelligible way bringing them to a state of Cold∣ness as to sense: I say Coldness as to sense; because as 'tis a Tactile Quality, in the popular acception of it, 'tis relative to our Organs of Feeling; as we see that the same luke-warm water will appear hot and cold to the same mans hands, if,

when both are plung'd into it, one of them shall have been newly held to the fire, and the other be benum∣med with frost. And indeed the custom of speaking has introduced an ambiguity into the word Cold, which often occasions mistakes, not easily without much attention and sometimes circumlocution also to be avoided; since usually by Cold is meant that which immediately af∣fects the sensory of him that pro∣nounces a body Cold, whereas some∣times 'tis taken in a more general notion for such a Negation or Immi∣nution of motion, as though it o∣perates not perceivably on our sen∣ses, does yet upon other bodies; and sometimes also it is taken (which is perhaps the more Philosophical sense) for a perception, made in and by the mind, of the alteration produced in the Corporeal Organs by the operation of that, whatever it be, on whose account a body is found to be cold.

But the Discussion of these Points is here purposely omitted, as for o∣ther Reasons, so principally because they may be found expresly handled in a fitter place.